Conventionally, an air conditioner for a vehicle, for example, an electric vehicle in which it is difficult to secure a heat source for heating a vehicle compartment, is known to heat air blown into a vehicle compartment in a heat pump cycle (i.e., a vapor compression refrigerant cycle).
For example, Patent Document 1 and Patent Document 2 describe a heat pump cycle used for such kind of a vehicle air conditioner, in which a refrigerant cycle in a cooling operation and a refrigerant cycle in a heating operation are configured to be switchable. More specifically, in the heat pump cycle of Patent Document 1 and Patent Document 2, a refrigerant cycle is switched so that refrigerant absorbs heat from outside air at an exterior heat exchanger and releases the heat to the blown air at an interior condenser, to heat the blown air in the heating operation.
In the heat pump cycle of Patent Document 2, in the heating operation, refrigerant is pressurized through multiple stages by two compression mechanisms such as a low stage compression mechanism and a high stage compression mechanism. An intermediate-pressure gas-phase refrigerant is mixed with a refrigerant discharged from the low stage compression mechanism, and the mixed refrigerant is drawn into the high stage compression mechanism. That is, a gas injection cycle (i.e., an economizer-type refrigerant cycle) is set to improve a coefficient of performance (COP) in the heating operation.